What Lens Model does Blender use for Camera Tracking?
As far as I know Blender works with a pinhole camera matrix. Where an image is created by a projection of the 3d coordinates into a 2d plane.

k1, k2 etc are radial distortion coefficients. Blender does not deal with tangential distortion.
For a deeper explanation refer to the following links:
http://lfa.mobivap.uva.es/~fradelg/phd/tracking/camera.html
https://calib.io/blogs/knowledge-base/camera-models
3x4 camera matrix from blender camera
You can get more information also reading on OpenCV and camera calibration.